Method and means for switching the electron beam in magnetron type beam switching tubes



May 21, 1957 E 55 METHOD AND MEANS FOR SWITCHING THE ELECTRON BEAM INMAGNETRON TYPE BEAM SWITCHING TUBES Filed June 27, 1955 K F mo N m S M 0& l PM Wm T A E W .b V I E Q n a n L: I n 6 B 7&2 b A Q WE 7 b V n m kV. B

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2,793,318 Patented May 21, 1957 METHOD AND IVEANS FOR SWITCHING THEELECTRON BEAM 1N MAGNETRON TYPE BEAM SWITCHJNG TUBES Eric Seif,Philadelphia, Pa., assignor to Burroughs Corporation, Detroit, Mich, acorporation of Michigan Application June 27, 1955, Serial No. 518,104

11 Claims. (Cl. 315-21) This invention relates to magnetron typemultiple position beam switching tubes and particularly to means for anda method of reliably switching the electron beam in such tubes a singlebeam position per input switching signal.

Magnetron type multiple position beam switching tubes make use ofcrossed electrostatic and magnetic fields in their operation. Usuallythe magnetic field is provided by a hollow cylindrical magnet whose fluxpermeates the tube in lines which are substantially parallel to theelongated cathode in the spade-cathode region of the tube. Tubes of thisgeneral type are disclosed and claimed in the U. S. patent of Fan andKuchinsky No. 2,721,955, entitled Multiposition Beam Tube, and assignedto the assignee of the present application. This tube is furtherdescribed in Electronic Design of January 1954 in an article titled ANew Beam Switching Tube. Such tubes have three arrays of electrodessurrounding the elongated thermionic cathode. A cylindrical array ofsymmetrically disposed beam forming and locking electrodes, known asspade electrodes, surrounds the cathode and is concentric with respectto it. Each spade electrode is insulated from the other spade electrodesand is usually connected to a source of potential which is positive withrespect to the cathode through a spade impedance device which usually isa resistor. The spade electrodes are usually coextensive in length withthe electron emissive portion of the cathode and have a curved, usuallyU-shaped, transverse cross-sectional configuration. The open part of thespade faces outwardly with respect to the cathode.

An array of symmetrically disposed electron receiving or targetelectrodes surrounds the spades and constitutes the outer array ofelectrodes of the tube. In most cases, the target electrodes are equalin number to the spade electrodes and each target is aligned with thespace between two adjacent spades whereby electrons which pass throughthe space may impinge on the target electrode which is associatedtherewith. Usually each target electrode, like each spade, is connectedto a source of potential which is positive with respect to the cathodethrough an impedance member which is usually a resistor. The outputsignal from each target electrode then may be developed across itstarget impedance member.

The third array of electrodes comprises a plurality of rodlike beamswitching electrodes which are equal in num her to the number of spades.Normally, each of the switching electrodes is disposed between an edgeof a spade and an adjacent target. The beam switching electrodes arenormally maintained at a positive potential, and this potential isreduced to enable the switching electrode to change the beam from alocked-in position at one spade to a locked-in position on the nextadjacent spade.

When all of the spades are at the potential of the spade power supply,the relationship between the electrostatic and magnetic fields is suchthat electrons emitted from the cathode follow curved paths around thecathode and substantially no electrons impinge on the spades or otherelectrodes of the tube. If, however, the potential on only one of thespades is lowered to, or near to, the

potential of the cathode, the configuration of the electrostatic fieldis changed, especially in the vicinity of the spade having the loweredpotential, and a stream or beam of electrons is formed between thecathode and the opening between the two spades at different potentialsto impinge partially upon the leading edge of that spade with thereduced potential. The edge of the spade to which the beam is attractedis determined by the direction of rotation of the electrons within thetube (which is determined by the polarity of the magnetic field whichpermeates the tube). The electron beam locks in at the edge of the spadewhich is furthest in the direction from which the electrons have come,i. e., furthest upstream in the electron flow, and this edge is calledthe leading edge. The opposite edge of the spade is the lagging edge.The electrons impinging on the leading edge of the spade cause electronflow through the spade impedance and, if the spade resistor value isproperly chosen, the electron flow therethrough maintains the reducedpotential of the spade sufiiciently to lock in the beam even though theexternal means for reducing the potential of the spade be removed.However, if .the switching electrode or grid upstream from where thebeam is locked in has its potential reduced, the electron beam which islocked on the earlier described spade (and which also impinges on thetarget electrode associated with that spade) changes its shape. If thereduction in potential on the switching electrode is sufficient, thebeam will spread as the electrons flow from cathode to target to theextent that part of the electrons of the beam impinge on the adjacentspade with which the switching electrode is associated, causing avoltage drop on that adjacent spade. Because of the tendency of theelectron flow to be curved by the magnetic field as previouslymentioned, the beam then switches to this adjacent spade which has alowered potential and which is further upstream along the electron beam.It should be noted that the direction of rotation of the beam also is inthe upstream direction, relative to electron flow from cathode to targetin crossed magnetic and electric fields.

Such tubes find considerable use in counters, as distributors, andgenerally as high-speed, multiple-position switches. A problem inreliability arises in the very speed and ease with which the switchingelectrodes or grids can spread the beam and cause it to switch whentheir potential is reduced. Unless precautions are taken, the beam willswitch more than one position around the tube.

One way to achieve single-step switching is to connect all switchinggrids in a common circuit and drive them with negative pulses which areclosely controlled as to amplitude and duration. If the pulse is belowminimums for width and amplitude, the beam will not switch at all. Ifthe amplitude is adequate, then the pulse width must be more than theminimum but less than the time required for more than one step of beamswitching. If the reduced potential were held on all grids for acomparatively long time, the beam would step rapidly from nectionincluding all even grids, and to drive these twoconnections with analternating voltage or Waveforms derived from opposite sides of aflip-flop circuit. In this way, the grids are driven in a push-pullmanner, and the next grid beyond the grid which is intended to switchthe beam always will have such a polarity voltage appl ed that it willinhibit more than the desired single switchlng step. Circuitry for thisbalanced or push-pull drive is less critical in the waveformrequirements than that for single-ended switching on all grids, but haslimitations such as encountered in variable frequencycounters," wherethe design of the push-pull drive circuitry which operates over a largefrequency range is critical and expensive. As a result hybrid circuitshave been developed for producing, with internal feedback, the gating ofunipolar pulses to alternate sets of switching-electrodes, such asdisclosed and claimed in the copending U. S. application filed by GeorgeG. Hoberg'on September 13, 1954, for Beam Tube Switching Circuits, S. N.455,546, and assigned to the assignee -of the present application. 7However, these prior art techniquesrequired large amplitude switchingsignals. In addition, where; variable scale counters are used fora resetto Zero after an odd count, the push-pull drive may result in aswitching signal on the wrong set of grids for a succeeding step,resulting in an erroneous count. This means that preset circuitry isnecessary for operation in response to zero set and external switchingsignals to assure proper variable scale counting operation. In suchoperation the count is slowed down by the necessity of presetting thecounter.

Therefore, a principal object of this invention is to provide animproved method of and means for controlling the electron beam in amagnetron beam switching tube.

Another object of this invention is a provide an economical and reliablemeans for switching the beam at single step from a unipolar pulseswitching signal.

A further object of this invention is to provide a simple and rapidvariable scale counter system utilizing a magnetron beam switching tubewith unipolar pulses for switching the beam, 21 single step withoutexternal preset.

In accordance with an embodiment of this invention, a magnetron beamswitching tube has a first group of alternate switching grids, hereafterreferred to as the even grids, connected together, and a second group ofalternate switching grids, hereafter referred to .as the odd grids,connected together. A first impedance network is connected to the targetelectrodes associated with the even grids, called the even targets, andprovides a common connection in the beam current path'from a positivevoltage supply to each of the even target. A second impedance network isconnected to the other target electrodes, associated with the odd gridsand called the odd targets, and provides a common connection in the beamcurrent path from a positive voltage supply to the odd targets. A diodecircuit is coupled with each of these common connections, to theirrespective switching grids, and to a common input circuit for switchingsignals, so that when the beam is held upon some particular target, beamcurent flows in a forward direction through the associated diodecircuit. This current injects current carriers into the crystallinestructure of a diode in the current carrying diode circuit. The otherdiode circuit also has a crystalline-structure diode but is notreceiving beam current and hence does not store current carriers untilthe beam is switched to a targe whose beam current path includes thisother diode circuit. When a voltage pulse sufiicient to cut off thediode circuits is applied to the input circuit, it encounters a highimpedance in the diode circuit not conducting current, but finds amomentarily low impedance in the crystal diode in which beam current hasinjected current carriers. These current carriers allow the pulse topass and to be applied to the associated switching grids, causingthe'beam to advance one step. circuit isolates the switching signal fromthe next switching grid, so only this single step occurs. As soon asthese current carriers are swept out, this crystal diode also presents ahigh back impedance to the pulse input circuit so that all switchinggrids are isolated from further volt- The high back impedance on theother diode switching tube with a generalized schematic circuit em-'bodying the invention;

Fig. 2 is a schematic view of a 'magnetron beam switching tube and anassociated specific circuit embodying the invention; and

Figs. 3a and 3b are simplified schematic diagrams of v specific circuitembodiments of this invention.

Referring to Fig. 1, there is shown in partial section view to simplifythe presentation, a magnetron beam switching tube 20 having an envelope22 and a centrally disposed elongated rod-like thermionic cathode 24,which is surrounded by an array of elongated spade electrodes 26, havinga generally U-shaped cross sectional configuration. An array ofelongated target electrodes 28 having an L-shaped cross-sectionalconfiguration surrounds the array of spade electrodes 26. The targetelectrodes 28 are equal in number to the spade electrodes, 26, and'eachtarget electrode 23 is disposed in alignment with the space between twoadjacent spades. An array of rod-like switching grid electrodes St) isdisposed between the array of spade electrodes 26 and the array oftarget electrodes 28, each of the switching grids being generallyaligned with respect to an edge of a spade electrode. About the envelope22 is a magnet 19 which causes a field, parallel with the cathode 24, topermeate the tube.

In the circuit which is shown in Fig. 1 each of the spades 26 isconnected to a source of positive potential IEt. The spade resistors 36may, if desired, be included within the tube envelope. Arranging thespade resistors 36 within the envelope results in a reduction of thestray capacitance of the tube and furthermore permits a reduction in thenumber of leads to be brought out to the base pins of the tube. Tubeswhich are designed for operation at high beam switching rates often havein ternal spade or target resistors, or both. The ohmic value of each ofthe spade resistors 36 is usually substantially the same, and is highenough that the voltage drop due to beam current passing therethrough,reduces the potential on the spade on which the beam impinges to, ornear to, the potential of the cathode'24 to thereby hold the beam in astable locked-in position. -Each target electrode 28 is connected to thepositive potential terminal +Et through individual targetimpedanceelements 40 which are illustrated as being resistors. The output signalfrom each beam position is developed across its targetresistor and istaken from the output terminal 56 of the beam position. The spadeimpedancesmay include elements other than resistors, but always includea resistance element which provides the directcurrent voltage drop'across theimpedance which is required to maintain the spade at a loweredpotential upon impingement of the beam and to lock in the electron beamat a particular spade.

[Alternate ones of the switching elements or grids 36 are connected totwo common leads 38 and 42. The common lead 42 is connected to thearbitrarily designated odd grids, and is coupled to a positivepotentialterminal ]E[; by the resistor 77b. Likewise the common lead 38is connected to the even grids and is coupledto the l-Eg terminal byresistor 77a.

Advancement of the electron beam from one beam position to anotheradjacent beam position is accom plished by applying a negative pulse tothe input terminal 75 which is coupled to both the common leads 38 and42, by respective diodes 74a and 74b. The input pulse potential may bedeveloped across the impedance element 76 coupling input terminal 75 tothe +Et terminal.

It is desirable to bias the switching grids 30 to the positive potentialat terminal +E which is chosen of such value that the beam remains in aposition upon any target and adjacent holding spade without spreading tothe advanced spade. While the actual switching grid pulse voltagerequired to reliably switch the electron beam by spreading the beam tothe leading spade may vary because of tube, magnetic field, or circuitconsiderations, pulses of 40 volts negative amplitude are average, butswitching with smaller pulses is possible and has been successfullyaccomplished. A negative pulse of 40 volts amplitude, for example,applied to the switching grids 30 would cause the electron beam 52 tofan out from the spade upon which the electron beam is locked in. As aresult of the fanning out of the electron beam adjacent to the edge ofthe spade 26 on which the beam is locked in, part of the beam impingeson the next adjacent or advanced spade which lies in the direction ofthe rotation of the beam. When part of the electron beam 52 impinges onthe advance spade the potential of that spade is dropped to, or near tothe potential of the cathode due to the beam current producing apotential drop across the spade load resistor and the electron beam thentransfers (or switches) and locks in on the advanced spade. Since thetime required for the beam to switch from one beam position to anothermay vary in accordance with tube geometry and circuit parameters, theduration of the 40 volts negative switching pulse must be controlledaccordingly with close limits it coupled to all the grids 30simultaneously. Thus, negative pulses of longer duration would result inthe beam switching more than one beam position.

However in accordance with the embodiment of the invention shown in Fig.1, even targets 2&2 have their resistors 40 in a common connection 70ato resistors 71a and voltage supply +Et. Another beam current path isfrom connection 70a through diodes 72a and resistor 73a for current fromvoltage supply +Et. Still another beam current path is through diode 72aas before, but then through diode 7 2a and impedance element 76.Impedance element 76 has a low resistance to direct current and a highreactance to alternating or pulse current or voltage. A choke coil wouldbe a typical element 76. Because impedance element 76 is of low ohmicresistance to direct current, the last mentioned path carries much ofthe beam current from supply +Et to target when the beam is on an eventarget. Diode 74a is a type of crystal diode in which current carrierstorage takes place, such as IN91 germanium junction diode, and thisbeam current stores current carriers therein. Similarly, odd targets 23bare connected through resistors 40 to common connection 7% and havethree beam current paths from voltage supply +Et. The path for most beamcurrent, when the beam is on an odd target, is through impedance element'76, diode 74b and diode 72b. Diode 7411 also is a crystal diode capableof current carrier storage, such as an 1N91. Beam current from supply+El; to an odd target will store current carriers in diode 7417. Evennumbered switching grids 30a are coupled to the junction of diodes 72aand 74a, and resistor 73a, through capacitor 79a. Grids 30a areadditionally connected to bias voltage +Eg through resistor 77a, shuntedby diode 73a. Similar connections are made from the odd grids Sill), tothe junction of diodes 72/), Mb and resistor 7317 through capacitor 7%;and thus the odd grids 30b are connected to bias voltage +i3 throughresistor 77b shunted by diode 7 Sb.

The circuit of Fig. l operates as follows: presume an even target 28a isreceiving the beam diodes 72a and 74a will be conducting; no currentflows through diodes 72b and 74b. A negative trigger pulse is applied toinput c 5 terminal 75 and results in a negative-going leading edge,which is applied to the anodes of diodes 74a and 74b. This pulse is ofsuflicient amplitude to cut ofl both diodes 74a and 72a. However, diode74b is not conducting substantially. When the beam current which hadbeen flowing through diode 74a is interrupted, the current carriers ithas stored will cause reverse current to flow through diode 74a anddevelop a large negative voltage pulse across resistor 73a. This voltageis coupled through capacitor 79a to the even grids 30a. has not beenconducting it will present a high impedance to the negative-going pulse,no current will flow through it, and negligible signal voltage will bedeveloped across resistor 73b. The negative pulse applied to even grids30a causes the beam to advance to the next, odd position in the tube.Resistors 71a and 71b are comparatively low in ohmic value, about 3,000ohms each, so the transfer of the beam from even to odd targetelectrodes does not produce enough signal at the grids to cause unwantedswitching.

Conversely, with the beam on an odd target 28b, beam current will flowthrough diode 74b and the odd branch will respond to the next pulse froma pulse generator connected to terminal 75, resulting in a negativepulse on the odd grids 30] causing the beam to advance one switchingstep. As with the even branch, the negativegoing pulse cuts off bothconducting diodes 72b and 74b in the branch carrying beam current.

Thus, when either diode 72a or 72b cuts off, the associated targets 23!;or 28b will have only resistors 71a or 711) conducting current tovoltage supply +Et- This presents a higher resistance path for beamcurrent, resulting in a slightly lower target potential. While thisetfect is slight, it does assist the negative pulse upon the associatedswitching grids to produce a rapid and reliable stepping of the beam. Itis a characteristic of magnetron beam switching tubes that, for a givenspade voltage, switchingof the beam can be achieved by adequatelyreducing either target or switching grid voltage, or both.

Accordingly, it is seen that diodes 74a and 74b function to direct theswitching pulses from terminal 75 to the appropriate set of odd or evenswitching grids of tube 20. Not only do these diodes 74a and 74b directthe energy of switching pulses in the appropriate direction, but theyperform this function with a net power gain. Because of this power gain,such circuits are properly considered as Diode Amplifiers. The physicalprinciples underlying diode amplifiers are described in detail in anarticle Diode Amplifier in National Bureau of Standards Technical NewsBulletin of October 1954, volume 38, Number 10. Briefly, this amplifyingphenomenon may be visualized by examining the circuit of Fig. l for theeven targets and grids when the beam is on an even target. Assume that atypical beam current of eight (8) milliamperes is flowing throughresistor 40, and that about five (5) milliamperes of this current isflowing through diode 74a and impedance element 76, from voltageterminal +Et. From conventional considerations of passive circuitelements and network theory, one would expect that the current developedby the negative switching pulse on terminal 75 would cut off diode 74awhen this pulse current reached a peak value of five (5) milliamperes.Due to current carrier storage, however, it is found that cut-off doesnot occur until peak current from this switching pulse reaches about tentimes the five milliamperes of beam current, or fifty milliamperes.Accordingly the IR voltage drop which pulse current produces acrossresistor 73a is about ten times what would be developed by beam currentfrom target 23a. This diode amplification insures positive stepping ofthe beam a single step due to the vigorous pulse applied to theappropriate grid. The lack of beam current in the alternate branchinsuresthat the full diode back impedance is presented to the switchingpulse and thus pulse current is blocked from the other set of grids sothat no unwanted Since diode 7 db switching pulse is present, itprevents current through diode 74b. Thus a high-speed, reliable beamswitching circuit is provided for operation from unipolar or singleendedpulses at input terminal 75 at frequencies from to more than 100,000cycles per second.

As shown in Fig. 2 circuit elements embodied in one form of impedance 76are utilized to provide the direct current path for beam current and toprovide a pulse input to the junction of diodes 74a and 7 1-0. in Fig.2a, resistor 80 provides a direct current path from supply +Et; to thejunction point 75. Pulse transformer 81 receives the incoming switchingpulses.- The secondary winding of transformer 81 is in series withisolation diode 82. Diode 32 is polarized to pass only negative-goingpulses to diodes 74a and 74b and to thereby block beam current flow. Thesecondary winding of pulse transformer 81 is shunted by diode 83 andresistor 84, with diode 83 polarized to conduct for positive voltage atthe transformer terminal connected to diode 82. This shunting circuit isto prevent ringing of transformer 81, i. e. to prevent oscillation orovershoot of an applied pulse, so the pulse 85 upon application to inputterminal 75 at the junction of diodes 74a and 74b is a negative-goingpulse as shown. As previously described, only that diode carrying beamcurrent will allow a reverse current to pass the embodiment of Fig. 2where the impedance 76 is a transformer and associated elements is:resistors 40:5,600 ohms, resistors 71a and 71b=2,700 ohms, resistors 73aand 73b=15,000 ohms, resistors 77a and 77b=100,000'

ohms, coupling capacitors 79a and 79b=1,000 M. M. F, with +Et=75 voltsand +E =15 volts on a divider from +Et. Spade resistors 36 are 180,000ohms. Load resistor 80 is 1,000 ohms, damping resistor 84 is 2,700 ohmsand transformer 81 has a 3:1 step down ratio with a ferric core and 150turns in the primary. This circuit operates successfully with a 60 voltinput trigger signal at terminal 75. i

In Fig. 3a, resistor 86 provides the direct current path from supply +Etto diodes 74a and 74b. 'Vacuum tube 87 has its anode connected to theinput terminal 75' at the junction of diodes 74a and 74b and theirconnection to resistor 86. Tube 87 also has its cathode grounded, andits control grid biased to near cut-off by a battery 89 and connected toinput terminal 88 for receiving positive-going switching pulses. When apositive pulse is the tube 37 becomes fully conducting-and the voltageat the junction of diodes 74a and 7% drops to a very low value, wellbelow the potential on the other side of diodes 74a and 74b. Dependingon whether an even or an odd target is conducting beam current, diode74a or 7412 will have stored current carriers and will allow this dropin potential-to pass through. This negative pulse then appears on theswitching grid associated with the target input terminal .75 at thejunction of diodes 74a and 74b,

to conduct beam current. Resistor 101 connects the cathode of tube 100to a negative voltage supply Elr.

Resistor 103 provides a direct current path forthc C011";

trol grid of tube 100 to keep the tube normally conductive and terminal75 substantially at +Et and coupling capacitor 102 connects this controlgrid to a terminal 104 When a negative-going for receiving negativepulses.

switching pulse is applied at terminal-104, tube 100 rises greatly inplate resistance and may even cut off. This causes the cathode of tube100 to approach the potential -Ek, and this negative-going pulse isapplied to the junction of diodes 74a and 74b. As described before, beamcurrent will have stored current'carriers in either diode 74a or 7%,depending on whether an even or odd target is receiving the beam. Whenthe negative pulse is ap-' plied to the junction of diodes 74a and'74b,the stored current carriers will pass reverse current and thereby passthis negative switching pulse to the proper switching electrode for thenext step.

From the above examinations of the several figures, it is seen that avariety of circuits can utilize the teachings of this invention. Theessentials are, that direct current paths be provided from +Et throughdiodes 74a and 7 4b to the even and odd targets, and that a pulse inputcircuit be connected to apply a negative switching pulse at the junctionof diodes 74a and 7411, with the appropriate switching grids coupled tothe 'other side of diodes 74a and 74b to receive an amplifier switchingpulse. Thus, a reliable beam switching circuit operable with singleendedinput trigger pulses is afiorded by the invention.

What is claimed is:

1. In combination, a magnetron beam switching tube comprising acentralcathode, an inner circle of spade electrodes, an intermediatecircle of switching electrodes aligned respectively with one side ofsaid spade electrodes, and an outer circle of target electrodes coveringthe spaces between spade electrodes, a first common connection toalternateswitching electrodes,a second common connection to the otherswitching electrodes, impedance means connecting the target electrodesand a positive voltage supply, a third common connection in theimpedance .means connecting together those target'electrodes associatedwith saidalternate switching electrodes, a fourth common connection inthe impedance means connecting together those target electrodesassociated with said other switching electrodes, a pulse input circuitincluding a circuit path for direct current and crystal diode circuitmeans operable to store current carriers, said pulse input circuitinter-connecting both of said common target connections with saidcircuit means to conduct beam current from said voltage supply, and acircuit connecting the pulse input circuit with both of said commonswitching electrode connections to apply pulses from said pulse inputcircuit to one of said common connections to switching electrodes onlywhen beam current is flowing through the diode circuit meansinterconnecting a particular common target connection and the pulseinput circuit and said'current is storing current carriers therein.

2. A combination as defined in claim 1 wherein the pulse input circuitcomprises a pulse transformer winding, diode and resistor circuit meansshunting said transformer winding to provide negative output pulses, andadditional impedance means shunting said transformer and said diode andresistor circuit means to provide a parallel direct current paththerewith.

3. A combination as defined inclaim '1 wherein the pulse input circuitcomprises impedance means including a direct current path, an amplifierconnected to said impedance means to apply pulse voltage thereto, and aninput circuit to drive said amplifier with switching pulses to increasethe current conduction of said amplifier.

4. A combination as defined in claim 1 wherein the pulse input circuitcomprises an amplifier having at least an output and control electrode,connected to conduct beam current, and an input circuit connected to thecontrol electrode of said amplifier to apply switching signals theretoto increase the resistance thereof.

5. Magnetron beam switching means as defined in claim 1 wherein saidimpedance means are resistors, said diode circuit means'includes aplurality of circuits and each circuit includes a plurality of diodesone of which plurality is a crystal diode capable of carrier storage,and

including a source of unipolar switching pulses connected to said pulseinput circuit.

6. Magnetron type beam switching means comprising a magnetron beamswitching tube having a cathode, a plurality of spade electrodes, aplurality of switching electrodes and a plurality of target electrodes,first impedance means connecting first alternate targets to a positivevoltage supply and having a first point therein common to all the firstalternate targets, second impedance means connecting the other alternatetargets to a positive voltage supply and having a second point there incommon to all the other alternate targets, an impedance device, a pulseinput circuit connected by said impedance device to said positivevoltage supply, first circuit means connected to said first alternatetargets and including first diode means, means commonly con necting saidfirst diode means to said pulse input circuit and to the switching gridsassociated with said first alternate targets, and second circuit meansconnected to said second alternate targets and including second diodemeans, and means commonly connecting said second diode means to saidpulse input circuit and to the switching grids associated with saidother alternate targets, said diode means being polarized to conductbeam current and so constructed as to store current carriers thereinwhen beam current flows.

7. A beam switching circuit for a magnetron beam switching tube having acathode, spades, switching grids and targets, a source of positivevoltage, said switching circuit comprising a resistance networkconnecting said targets to said source of positive voltage, a networkconnecting said switching grids in two sets of alternate grids, meansbiasing the switching grids to such value that the beam remains inposition upon any target without spreading, a first crystal-diodeconnecting to a point in said resistance network common to a first setof alternate targets corresponding to one set of alternate grids andcoupled to the set of alternate switching grids associated with saidfirst set of atlernate targets, a second crystaldiode connecting to apoint in said resistance network common to the other set of alternatetargets and coupled to the other set of alternate switching grids, anda. two terminal pulse input circuit including a direct current path andconnecting to both said diodes at one terminal and to said source ofpositive voltage at the other terminal, said crystal diodes beingpolarized to conduct beam current and so constructed as to store currentcarriers when beam current flows.

8. in combination, a magnetron beam switching tube having a cathode,spades, targets and switching grids, a switching circuit responsive tounipolar pulses and comprising resistors connected one to each of saidtargets, a first common connection of all resistors connected to a firstset of alternate targets, a second common connection of all resistorsconnected to the second set of alternate targets, crystal diodesconnected to said common connections to conduct electron beam currentfrom said targets to a common point and to store current carriers whensaid electron beam current flows, an impedance element connecting saidcommon point to a source of positive voltage to conduct electron beamcurrent, a third common connection of all switching grids associatedwith said first set of alternate targets, coupling means connecting saidthird and said first common connections, a fourth common connection ofall switching grids associated with said second set of alternatetargets, coupling means connecting said second and fourth commonconnections, and a resistive network connecting said switching grids toa source of positive bias voltage.

9. Magnetron type beam switching means comprising a magnetron beamswitching tube having an axial cathode, a plurality of beam controllingspade electrodes arranged along the path of electron beam current fromsaid cathode in a position most proximate to said cathode along saidpath, a plurality of target electrodes positioned along the path ofelectron beam current more remotely from said cathode, a plurality ofswitching electrodes in a position along said beam current pathintermediate between said spade electrodes and said target electrodes,first impedance means for connecting a first set of alternate targets toa positive voltage supply and having a first common point therein,second impedance means for connecting the other set of alternate targetsto a positive voltage supply and having a second common point therein, apulse input circuit connected to a positive voltage supply and includinga direct current path, first crystal diode circuit means connected tosaid first common point and to said pulse input circuit and coupled tothe switching grids associated with said first set of alternate targets,second crystal diode circuit means connected to said second common pointand to said pulse input circuit and coupled to the switching gridsassociated with said other set of alternate targets, said crystal diodecircuit means being polarized to conduct beam current and to storecurrent carriers therein when beam current flows, and a source ofswitching pulses connected to said pulse input circuit.

10. In a beam switching system which includes a magnetron beam switchingtube, having a cathode, a plurality of spade electrodes, a plurality ofswitching electrodes and a plurality of beam receiving electrodes, thecombination comprising first resistive means connecting at least onebeam receiving electrode to a positive voltage supply, a diode andsecond resistive means connecting to an intermediate point of said firstresistive means and to said positive voltage supply to conduct beamcurrent, a pulse input circuit including a direct current paththerethrough and connected to said positive voltage supply, a crystaldiode connecting between said diode and said'input circuit to conductbeam current and to store current carriers, coupling means connectingthe switching electrode associated with said beam receiving electrode tothe junction between said diode and crystal diode, and third resistivemeans connecting said switching electrode to a source of positive biasvoltage.

11. In combination, a magnetron beam switching tube comprising a centralcathode, an inner circle of spade electrodes, an intermediate circle ofswitching electrodes aligned respectively with one side of said spadeelectrodes, and an outer circle of target electrodes covering the spacesbetween spade electrodes, a first common connection to one group ofperiodically disposed switching elec trodes, a second common connectionto another group of periodically disposed switching electrodes,impedance means connecting the target electrodes and the spadeelectrodes and a positive voltage supply, a third common connection inthe impedance means connecting together one group of those electrodesassociated with said one group of switching electrodes, a fourth commonconnection in the impedance means connecting together another group ofthose electrodes associated with said another group of switchingelectrodes, a pulse input circuit including a circuit path for directcurrent and unidirecctionally conductive circuit means operable to storecur- References Cited in the file of this patent UNITED STATES PATENTSHolden et a1. Apr. 6, 1943 Depp June 3, 1952

